1. Field of the Invention
The invention relates to an output capacitor array of a switched-mode power supply, having at least two individual capacitors being connected electrically in parallel, a solid negative-pole metal rail, and a solid positive-pole metal rail being electrically insulated from the negative-pole metal rail, for carrying direct current.
Such an array and a switched-mode power supply that contains the capacitor array is known from German Petty Patent G 90 07 402.
The switched-mode power supply described therein has a wide ribbon cable on the secondary side of a transformer, that is passed as a secondary winding around one leg of the transformer and, with the interposition of a rectifier configuration, is passed as a parallel-guided flat twin cable through core parts of a smooth inductor to output terminals. An output capacitor in the form of a plurality of parallel-connected capacitors is disposed in a region between the smoothing inductor and the output terminals. The capacitors are disposed on one of the ribbon conductors or between the two ribbon conductors and are electrically connected to them.
The capacitor array according to the invention is suitable for use as an output capacitor in such a switched-mode power supply, but is also suitable for use in other switched-mode power supplies.
In switched-mode power supplies with a high switching frequency and a one-stage output filter, filter capacitors are needed that have the lowest possible equivalent series resistance or ESR, for instance less than one milliohm, relative to the entire capacitor bank. If the frequencies to be filtered are high, such as 50 to 500 kHz, then not only the ESR but especially the equivalent series inductance or ESL of the capacitor has a decisive influence. ESL values&lt;1 nH, for instance, are required for the overall capacitor array. If a plurality of capacitors are connected in parallel, those requirements must be taken into account, as must the fact that a uniformly high alternating current load of the individual capacitors should be attained. In switched-mode power supplies with high output currents, the capacitors must be connected to solid copper rails, while maintaining the inductance conditions.
With the filter configuration known from German Petty Patent G 90 07 402, such requirements cannot be met satisfactorily. In particular, the capacitors are not connected in an adequately low-inductance way.